Method of improving the color of pulp



. the eye and Patented May 31, l927.

UNITED STATES FRANCIS G. RAWLING. F KNOXVILLE, TENNESSEE.

IETHOD 0F IMPROVING THE COLOR 0F PULP.

No Drawing.

This invention relates to a process of lightening the color of paperpulp materials after they have become darkened due to combination oforganic acids with the iron of the apparatus used.

In processes of obtaining pulp from chestnut wood, in which the wood,either before orafter the extraction of tannic acid, is treated withsolutions of cookingchemical which are neutral or mildly alkaline, andin which the chemically treated wood is further submitted to grinding,pulping, heating or other form of disintegration in iron or steelmachines, a dark colored pulp is obtained. The color is due to thereaction of the tannic acid which is present in the wood with the ironor steel parts of the disintegrating devices. The color of the pulp, andpaper made from it, is black or dark grey, the color being darker, thegreater the amount of tannic acid present, and the longer the contact ofthe ulp with the iron or steel surfaces. This co or is objectionable andefiorts have been made to make this color lighter or change it to abrown color.

I ave discovered that the chemicall treated chestnut wood chips may be.pulpe ground, beaten or disintegrated in the presence of an oxide orhydroxide of one of the alkaline earths, as for example, with calcium orstrontium or barium hydroxide. The oxides of the alkaline earths may beused, since they combine with. water very readily to form thehydroxides, and when dissolved in the water, they are resent ashydroxides. Furthermore, the a dition of such oxides, or hdydroxides ofthe alkaline earths may be ma e to the pulp subsequently to the o rationof pulping, grinding, beating or 'sintegrating, either when t e is beingwashed, or when the pulp is being made into paper. The oxides andhydroxides of the alkaline earths may be added to the suspension of thepulp in water as it enters the paper machine.

The black coloring material present in the pulp is a compound ofiron'and tannic acid.

y mixing lime with the pulp. for example, a reaction takes place, inwhich the calclum salt of tannic' acid is formed together with ferrichydroxide. Both of these substances are brown in color, and the color ofthe pulp and paper after treatment with the lime,-

brown, which is more pleasing to is a 11g is quite slmilanm color togrades Application filed September 1, 1926. Serial No. 133,085.

of paper known as kraft and wrapping in" the paper industry.

It will be observed that the terms oxide and hydroxide are usedinterchangeably and the reason for this will be obvious from the mannerof use. During the operation of a process any oxide present quickly isconverted to hydroxide in its intermingled contact with the watersolutions in the apparatus.

1. In the pulping of vegetable fibrous material containing organic acidsthe process of making lighter the color'of the pulp after it has beentreated with apparatus containing parts formed of iron and dark colorediron and acid compounds have been formed, which process comprises addingan oxide of an alkaline earth to the pulp and effecting a reactionbetween the alkaline material and the acid' and the formation of ferrichydroxide with resulting lightening of color.

2. In the pulping of vegetable fibrous material containingtannic acidthe processo making lighter the color of the pulp after it has beentreated mechanically with apparatus containing iron parts and darkcolored iron and acid compounds have been formed in the pulp, whichprocess comprises addingcalcium oxide to the pulp and effecting areaction between the calcium material and the acid and the formation offerric hydroxide with resulting lightening of color.

3. In the pulping of chestnut wood after it has been subjected tomechanical treatment in apparatus having iron parts in contact with thechestnut pulp and dark colored compounds of iron and tannic acid havebeen formed which process comprises adding an oxide of an alkaline earthto the pulp and thereby efl'ecting a reaction between the alkalinematerial and the chestnut wood tannicacid, and the formation of ferrichydroxide with resulting lightening of color.

4. In the pulping of chestnut 'wood after it has been subjected tomechanical treatment in apparatus having iron parts in con- 10 tact withthe chestnut pulp and dark colored compounds of iron and tannic acidhave been formed which process comprises adding a calcium oxide to thepulp and thereby efiecting a reaction between the calciumoxide and thechestnut wood tannic acid and the formation of ferric hydroxide withresultin lightening of color.

11 the pulping of vegetable fibrous material containing tannic acid andwhich material has been subjected to chemical treatment and tomechanical disintegration in apparatus containing iron and dark colorediron and acid compounds have been formed in the pulp, which processcomprises adding an oxide of an alkaline earth to the pulp and effectinga reaction between the alkaline material and the acid and the formationof ferric hydroxide with resulting lightening of color.

In testimony whereof I afiix my signature.

FRANCIS G. RAWLING.

